This invention relates to an artificial or prosthetic foot. More particularly, this invention relates to a prosthetic foot which incorporates improved energy storing capabilities by using an auxiliary deflection plate. Still more particularly, this invention relates to a lightweight prosthetic foot which, with its energy storage capabilities, provides a smooth natural motion for the user. Still more particularly, this invention relates to a prosthetic foot having an improved keel, spring structure, and method of manufacture which provides a lightweight, easy-to-use, yet sturdy S.A.C.H. prosthetic foot.
A number of types of prosthetic feet are known to the art which attend to various problems relating to the structure, cosmetic appearance, weight, and energy storage and transfer characteristics of the foot. An early design of a prosthetic foot incorporated a leather hinge across the ball of the foot with natural rubber positioned in a v-groove above the hinge. In use, the rubber member was compressed to store energy for the next step of the user. Later examples of such feet utilized various elastic materials acting as springs and energy absorbers. Thus, the notion that energy storage capabilities within a prosthetic foot could be advantageous to an amputee is not new. Such a device today is unsatisfactory because of its weight at the furthest point from the knee center which creates a large moment resulting in high stresses about the knee and greater impact at full extension of the leg. Moreover, such a device does not provide the amputee with sufficient energy storage capabilities and is unacceptable cosmetically.
Another prosthetic foot introduced about 1960 included an inner keel of wood surrounded by flexible foam plastic. The plastic has a sufficient density to permit limited resistance to bending, thus creating some energy storing characteristics. Later devices have improved upon this design by carving keels from solid, homogeneous plastic blocks in an effort to relieve some of the stresses on the flexible foam plastic and to allow somewhat greater energy storage characteristics. However, these solutions have not proven to be completely satisfactory because of the weight of the foot and the eventual failure of the flexible foam urethane. In U.S. Pat. No. 4,177,525 an artificial foot construction is shown as having a rigid keel made from a molded plastic material with a metal reinforcing strip embedded within the plastic keel portion near the lower surface. The keel is surrounded by a typical flexible foam plastic material molded to the keel to form the outer surface of the foot. While this device has proven to be commercially acceptable, it remained a problem in the art to improve upon that artificial foot by incorporating significantly improved energy storing capabilities, and selecting materials which made the device lightweight, yet sturdy, and capable of a long commercial life.
In U.S. Pat. Nos. 3,484,871 and 3,766,569 the concept of utilizing leaf springs in an artificial foot is shown. An artificial foot having a solid inelastic core preferably made of wood extends substantially the entire height of the foot. A front core portion extends forwardly of the main core to receive an upwardly-offset, flat, spring seat for receiving a flat, elastic leaf spring made from a pair of spring plates of uniform gauge, width, and length, and arranged in a laminar form. A flexible plastic liner, preferably made of Teflon brand material, is interposed between the plates. The strength and gauge of the spring plates is such that when the foot is flexed, such as when the weight of the wearer shifts forward over the ball of the foot in walking, the spring will flex about the ball of the foot and maintain its elastic properties to restore the toe of the foot to its original position after each walking step when the weight of the wearer is released. A protective webbing material, such as a Nylon brand material, is fitted between the lower spring plate and the sole to reduce wear, while the foot is surrounded by a resilient cover.
Thus, it is an aim in this art to provide a lightweight prosthetic S.A.C.H. artificial foot made from materials and constructed to exhibit favorable walking and running characteristics. To this end, attention is particularly given in this invention to an improved keel construction, the keel material, an improved spring construction, the spring material, and to a method of making the spring.
Notwithstanding those feet in the art, it has remained a particular problem to improve upon the energy transfer characteristics of the foot. Thus, is an overall objective of this invention to utilize an improved spring structure made from a composite material and having sufficient energy storing capability to meet the needs of the user.
It is another overall object of this invention to provide a lightweight prosthetic foot of the type described having a strong, yet lightweight, rigid compression molded composite keel.
It is still another object of this invention to provide a prosthetic foot of the type described which utilizes a laminate of a fiber-reinforced, carbon composite for the spring plates.
It is still another object of this invention to provide a prosthetic foot having a primary carbon-composite deflection plate and an auxiliary carbon-composite deflection plate for improving the energy storage and release characteristics of the foot, while ensuring its light weight.
These and other objects of the invention will become apparent from the detailed written description of the invention which follows, taken in conjunction with the accompanying drawings.